1. Field of the Invention
The present invention relates to a method for manufacturing an electro-optical device which can be readily scaled up into a large area. The electro-optical device according to the present invention is useful as a screen for shielding visual field of windows and show windows, as a light-control curtain, and as a liquid crystal display which displays and electrically converts characters, figures, symbols, and the like.
2. Description of the Prior Art
Liquid crystal display devices heretofore used widely in practice include those using nematic liquid crystals, i.e., the TN (twisted nematic) mode or the STN (super-twisted nematic) mode liquid crystals. There has also been proposed recently a liquid crystal display device using a ferroelectric liquid crystal. However, it is requisite for the devices mentioned above to use a polarizer sheet and to impart molecular orientation so that the liquid crystal molecules may arrange regularly along one direction. On the other hand, there is also known a dispersion type liquid crystal device which realizes a bright display having a high contrast without using any polarizer sheets nor applying such an orientation treatment to the molecules. A dispersion type liquid crystal device comprises a transparent solid polymer having dispersed therein nematic, cholesteric, or smectic liquid crystals in granules or in sponges. A method for fabricating such a liquid crystal device comprises dispersing liquid crystals in a polymer by encapsulating the liquid crystal, and then applying the resulting polymer as a thin film on a substrate or a film. The substances proposed to use in the encapsulation include gelatin, gum arabic, polyvinyl alcohol, and the like.
According to the encapsulating technique set forth above, the liquid crystal molecules having encapsulated in poly(vinyl alcohol) arrange themselves along the electric field when an electric field is applied, provided that the molecules have a positive dielectric anisotropy in the thin film. In such a case, the thin film turns transparent if the refractive index of the liquid crystal is equal to that of the polymer. When no electric field is applied, the liquid crystal molecules are in random orientation. Thus, the thin film turns opaque since the light cannot be transmitted due to scattering. In addition to the one exemplified above, there are known also other liquid crystal devices comprising a thin film or a film of a polymer having dispersed therein encapsulated liquid crystals. For example, there is known a liquid crystal display device comprising an epoxy resin matrix having dispersed therein liquid crystal materials, a liquid crystal display device which utilizes phase separation between a liquid crystal and a photocurable substance, or a liquid crystal display device which comprises a three-dimensional polymer structure being impregnated with a liquid crystal. Those liquid crystal electro-optical devices described above are collectively referred to hereinafter as dispersion type liquid crystal devices.
One of the factors which determine the device characteristics of a dispersion type liquid crystal device is the area in which the liquid crystal is present. In a device comprising the liquid crystal in capsules, the degree of dispersion of these capsules is important; if the device is a one using a polymer, the degree of dispersion of the space within the polymer becomes of concern. It has been desired to achieve uniform dispersion of the liquid crystal, since a nonuniform dispersion of the liquid crystal causes heterogeneous transmission of the light in the display, which leads to an irregular image display or an uneven contrast.